1. Field of the Invention
This invention relates to the generation and display of stereoscopic images.
2. Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or implicitly admitted as prior art against the present invention.
Three dimensional (3D) or stereoscopic television has recently been made available to the consumer, and it is expected that the amount of 3D equipment and programming will increase rapidly in the next few years.
3D television relies on a stereoscopic technique whereby pairs of images are captured by respective cameras which are laterally displaced (that is, substantially in a horizontal image direction) by a certain distance, for example a typical spacing of a user's eyes. The pairs of images therefore represent slightly different views of the same scene; in general they will encompass the same items within the scene (except perhaps at the image extremities) but the relative positions of the items between the two images will depend on the distance of the items from the camera arrangement.
When the images are displayed, it is important that each of the user's eyes sees (at least mainly) a respective one of the image pair. In practice this is achieved in various ways, such as by the user wearing polarising, time multiplexing or colour-filtering spectacles, or by the television screen itself being provided with a special lens arrangement which diverts each of the two images to a respective eye position of the viewer. Of these, the colour-filtering technique, common in early attempts at 3D cinema, is not generally used in 3D television technology.
The time-multiplexing approach has been adopted by several leading 3D television manufacturers. It works by the television displaying rapidly alternating left and right images whilst each lens in the time-multiplexing glasses worn by the viewer blocks or passes light from the display when required. So, each lens of the glasses alternate between blocking and passing light in synchronism with the display of the image appropriate to that eye of the user. This results in the left eye of the user seeing only the left images and the right eye of the user seeing only the right images. Each 3D image pair is thus comprised of a pair of images, with each image from this pair displayed half an image period apart to a different eye. A display which works in this way is known as a sequential stereoscopic display.
One drawback of the sequential display system comes from the fact that each image from the stereoscopic image pair is conventionally captured at the same point in time. On the television, however, these images are displayed half an image period apart, to allow for the sequential nature of the glasses arrangement. The images for one eye are thus seen half an image period later than the images for the other eye. For images of fast moving objects, for example as part of sports coverage or video game play, the way in which the eyes and brain process this time disparity causes the user to incorrectly register depth for horizontally fast-moving objects and to incorrectly register misalignment for vertically fast-moving objects. This phenomenon is known as the “Pulfrich effect”.
As an example, consider a scenario where the images are of a fast-moving football, and where the right image of each 3D image pair is displayed with a half image period's delay with respect to the left image of that image pair. If the football is moving from the left to the right at a particular constant depth with respect to a background image, then the viewer will incorrectly perceive the football as being at a greater depth (in an arbitrary set of coordinates in which “greater depth” implies that an object is perceived to be closer to the viewer) than the intended particular constant depth. Conversely, if the football is moving from the right to the left at a particular constant depth, then the viewer will incorrectly perceive the football as being at a lesser depth (that is, appearing further away) than the intended particular constant depth. Also, if the football is moving vertically, the left and right images of the football will appear misaligned, providing the viewer with an image that is uncomfortable to look at.
The same phenomenon will occur if the left image is delayed with respect to the right image, except that, in this case, the football will (incorrectly) appear to be further away from the viewer as it moves from the left to the right and closer to the viewer as it moves from the right to the left.
This presents a problem in displaying fast-moving 3D images on a sequential stereoscopic display, in particular 3D sports coverage or video games, where accurately judging the depth of fast moving objects is very important.